There are many types of biometric algorithms presently known in the art. IrisCode is an example of such a biometric algorithm. IrisCode has had great success in biometric markets as a result of its strengths, including high matching speed, predictable false acceptance rate, and robustness against local brightness and contrast variations. A method of generating IrisCode and using the IrisCode features are disclosed in J. G. Daugman, “High confidence visual recognition of persons by a test of statistical independence”, IEEE Transactions on Pattern Analysis and Machine Intelligence, vol. 15, no. 11, pp. 1148-1161, 1993, the contents of which are incorporated herein by reference.
The obtaining of an IrisCode from an original image uses the “lesser than” i.e. “<” and the “greater or equation than” i.e. “≧” operators, thus retaining only the signs of the filter responses as features of biometric templates. This involves applying two-dimensional Gabor filters with zero DC globally to the whole of an original image in a dimensionless polar coordinate system denoted I0(ρ, φ), where ρ denotes the radial coordinate and φ the angular coordinate. The complex Gabor response is encoded into two bits (hRe and hIm) by using the following inequalities:
                              h          Re                =                              1            ⁢                                                  ⁢            if            ⁢                                                  ⁢                          Re              ⁡                              (                                                      ∫                    ρ                                    ⁢                                                            ∫                      ϕ                                        ⁢                                                                                            I                          0                                                ⁡                                                  (                                                      ρ                            ,                            ϕ                                                    )                                                                    ⁢                                              ⅇ                                                                              -                                                                                          (                                                                                                      r                                    0                                                                    -                                  ρ                                                                )                                                            2                                                                                /                                                      α                            2                                                                                              ⁢                                              ⅇ                                                                              -                                                                                          (                                                                                                      θ                                    o                                                                    -                                  ϕ                                                                )                                                            2                                                                                /                                                      β                            2                                                                                              ⁢                                              ⅇ                                                  -                                                      ⅈω                            ⁡                                                          (                                                                                                θ                                  0                                                                -                                ϕ                                                            )                                                                                                                          ⁢                      ρ                      ⁢                                              ⅆ                        ρ                                            ⁢                                              ⅆ                        ϕ                                                                                            )                                              ≥          0                                    (        1        )                                          h          Re                =                              0            ⁢                                                  ⁢            if            ⁢                                                  ⁢                          Re              ⁡                              (                                                      ∫                    ρ                                    ⁢                                                            ∫                      ϕ                                        ⁢                                                                                            I                          0                                                ⁡                                                  (                                                      ρ                            ,                            ϕ                                                    )                                                                    ⁢                                              ⅇ                                                                              -                                                                                          (                                                                                                      r                                    0                                                                    -                                  ρ                                                                )                                                            2                                                                                /                                                      α                            2                                                                                              ⁢                                              ⅇ                                                                              -                                                                                          (                                                                                                      θ                                    o                                                                    -                                  ϕ                                                                )                                                            2                                                                                /                                                      β                            2                                                                                              ⁢                                              ⅇ                                                  -                                                      ⅈω                            ⁡                                                          (                                                                                                θ                                  0                                                                -                                ϕ                                                            )                                                                                                                          ⁢                      ρ                      ⁢                                              ⅆ                        ρ                                            ⁢                                              ⅆ                        ϕ                                                                                            )                                              <          0                                    (        2        )                                          h          Im                =                              1            ⁢                                                  ⁢            if            ⁢                                                  ⁢                          Im              ⁡                              (                                                      ∫                    ρ                                    ⁢                                                            ∫                      ϕ                                        ⁢                                                                                            I                          0                                                ⁡                                                  (                                                      ρ                            ,                            ϕ                                                    )                                                                    ⁢                                              ⅇ                                                                              -                                                                                          (                                                                                                      r                                    0                                                                    -                                  ρ                                                                )                                                            2                                                                                /                                                      α                            2                                                                                              ⁢                                              ⅇ                                                                              -                                                                                          (                                                                                                      θ                                    o                                                                    -                                  ϕ                                                                )                                                            2                                                                                /                                                      β                            2                                                                                              ⁢                                              ⅇ                                                  -                                                      ⅈω                            ⁡                                                          (                                                                                                θ                                  o                                                                -                                ϕ                                                            )                                                                                                                          ⁢                      ρ                      ⁢                                              ⅆ                        ρ                                            ⁢                                              ⅆ                        ϕ                                                                                            )                                              ≥          0                                    (        3        )                                          h          Im                =                              0            ⁢                                                  ⁢            if            ⁢                                                  ⁢                          Im              ⁡                              (                                                      ∫                    ρ                                    ⁢                                                            ∫                      ϕ                                        ⁢                                                                                            I                          0                                                ⁡                                                  (                                                      ρ                            ,                            ϕ                                                    )                                                                    ⁢                                              ⅇ                                                                              -                                                                                          (                                                                                                      r                                    0                                                                    -                                  ρ                                                                )                                                            2                                                                                /                                                      α                            2                                                                                              ⁢                                              ⅇ                                                                              -                                                                                          (                                                                                                      θ                                    o                                                                    -                                  ϕ                                                                )                                                            2                                                                                /                                                      β                            2                                                                                              ⁢                                              ⅇ                                                  -                                                      ⅈω                            ⁡                                                          (                                                                                                θ                                  0                                                                -                                ϕ                                                            )                                                                                                                          ⁢                      ρ                      ⁢                                              ⅆ                        ρ                                            ⁢                                              ⅆ                        ϕ                                                                                            )                                              <          0                                    (        4        )            where r0, θ0, ω, α and β are the parameters of the Gabor filters. r0 and θ0 respectively denotes the location of the filter, ω denotes the Gabor wavelet frequency, and α and β are parameters controlling the wavelet size. Re(A) denotes the real component of A while Im(A) denotes the imaginary component of A.
Many methods developed for biometrics use the computational core of IrisCode. These methods typically replace the usage of Gabor filters as is done in Equations 1-4 with other forms of linear filters or functions. Examples of such biometrics are PalmCode for palm print recognition which is disclosed in D. Zhang, W. K. Kong, J. You and M. Wong, “On-line palmprint identification”, IEEE Transactions on Pattern Analysis and Machine Intelligence, vol. 25, no. 9, pp. 1041-1050, 2003, or Ordinal Code for iris recognition which is disclosed in Z Sun and T. Tan, “Ordinal measures for iris recognition”, IEEE Transactions on Pattern Analysis and Machine Intelligence, vol. 31, no. 12, pp. 2211-2226, 2009.
These biometric methods essentially are feature extraction algorithms. The filtering and binarization processes may cause too much information inherent in the original biometric images to be lost, thus making the obtaining of biometric images from the biometric features generally unfeasible. As a result, original or compressed versions of the original images have to be stored so as to provide an image for reference and/or upgrading biometric systems. An example of this is in the case of IrisCode where the original iris images may be stored to allow for upgrading iris recognition systems.
It is an object of the present invention to provide a method of generating images from biometric features and devices which address at least one of the problems of the prior art and/or to provide the public with a useful choice.